Here's my take on the best possible Regulan cavalry company using canon designs meeting the 5/8 minimum speed criterion. It contains several duplicate designs, but I include alternates in the write-ups below.
Command Lance
HRC-LS-9001 Hercules: 5/8/0, XLE, 197, 24, ER PPC, LB 10-X, Strk-2 x2, Pul Med, Pul Sm x2(R)
GRF-3M Griffin: 5/8/5, XLE, 160, 26, ER PPC, LRM-20, Sm Laser
TBT-3C Trebuchet: 5/8/0, XLE, CASE, LRM-15 w/ FCS x2, Med Las x4
TBT-3C Trebuchet: 5/8/0, XLE, CASE, LRM-15 w/ FCS x2, Med Las x4
The command lance is essentially a fire support lance, capable of throwing 80 LRMs (the two Trebuchets and the Griffin) a turn, of which 60 are Artemis-enhanced. These are supplemented by two ER PPCs and an LB 10-X AC (the Hercules and Griffin), for modest hole-punching and crit-seeking. Opponents that close will face a fusillade of eight medium lasers on the Trebuchets, along with four Streak tubes and a pulse medium laser on the Hercules. The Hercules and Griffin offer three small lasers for limited anti-infantry capability.
The Trebuchets are on the Regulan RAT in FM: 3085, and are likely imported from Kali-Yama on the independent world of Kalidasa, based on the factories in Obj: FWL. The Hercules is on the former FWL RAT in FM: 3085, and also likely imported from Kali-Yama based on Obj: FWL. The Griffin is also on the former FWL RAT in FM: 3085, but no one produces Griffins in Obj: FWL, so it is likely a Jihad survivor.
Alternates for one of the -3C Trebuchets on the former FWL RAT in FM: 3085 include the -7M Trebuchet and the -7M Shadow Hawk, but these suffer from a NARC launcher and a Light Gauss Rifle, respectively. Personally, I'd stick with the two -3C Trebuchets to maximize the Artemis-enhanced missile volley.
Cavalry Lance
SKW-2F Shockwave: 5/8/0, XLE, 160, 22, LRM-10 w/ FCS, ER Large, RAC-5
OST-2Mb Ostwar: 5/8/0, XLE, 192, 36, ER Large x3, SRM-6 x2
OST-2Mb Ostwar: 5/8/0, XLE, 192, 36, ER Large x3, SRM-6 x2
WVR-7M Wolverine: 5/8(10)/5, XLE, 160, 24, ER Large x2, Pul Med x2, SRM-6
The Cavalry Lance carries the bulk of the company's direct, ranged firepower, including no less than nine ER large lasers (spread among all four mechs) and a RAC-5 (on the Shockwave), supplemented by an Artemis-enhanced LRM-10 (also on the Shockwave). After punching a lot of holes in enemy armor while closing, the Cavalry Lance can those holes and score crits with 30 SRM tubes (on the two Ostwars and Wolverine) and two pulse medium lasers (on the Wolverine).
The OST-2Mb is not the Ostwar variant that shows up on the Regulan RAT in FM: 3085, but according to Obj: FWL, the Regulans have two Ostwar factories (Harmony Metal Works and Ronin, Inc.). With two Ostwar factories, I assume that the Regulans can produce the far superior OST-2Mb variant. Both the Shockwave and Wolverine show up on the former FWL RAT in FM: 3085, but are no longer produced in former FWL space according to Obj: FWL, so they must be Jihad survivors.
The -2Mb Ostwar is a Flashman on steroids, and it's hard to go wrong with two of them. But if you must, I'd go with the ANV-5M Anvil, which carries two ER large lasers, four medium lasers, and ECM, which is superior loadout to other Ostwar variants. The PXH-3M Phoenix Hawk is another possibility with two ER large lasers. Both the Anvil and P-Hawk show up on the former FWL RAT in FM: 3085.
Shock Lance
BTZ-3F Blitzkrieg: 7/11/0, XLE, 116, 20, Ultra AC/20
BTZ-3F Blitzkrieg: 7/11/0, XLE, 116, 20, Ultra AC/20
SCB-9T Scarabus: 10/15(17)/0, XLE, 99, 20, ECM, TAG, 10, TSM, Hatchet, Med Las x2, Sm Las x2
SCB-9T Scarabus: 10/15(17)/0, XLE, 99, 20, ECM, TAG, 10, TSM, Hatchet, Med Las x2, Sm Las x2
The Shock Lance is a close combat lance, designed to outflank or drive straight through enemy formations at high speed and then disrupt and cripple them with two Ultra AC/20s (the Blitzkriegs) and TSM-enhanced hatchet strokes and medium/small laser arrays (the Scarabuses). The Scarabuses can also call in Arrow IV or TAG-enhanced LRM fire (load the Griffin in the Command Lance appropriately) using their TAG units, or allow the Shock Lance to attack from ambush using their ECM suites.
They are imported from the Lyrans, but the Blitzkreig and Scarabus figure highly in the Regulan RAT in FM: 3085. No doubt the Lyrans are propping up the Regulans against other former FWL states closer to the Lyran border, and these Lyran designs better fit the Regulan style of combat than traditional FWL designs.
Again, I'd stick with two Blitzkreigs and two Scarabuses -- two Ultra AC/20s and two TSM-enhanced hatchets are much more effective at opening holes in armor and persuading the enemy to move elsewhere than one of each. But if you must replace one Blitzkreig, the HER-5Sr Hermes II is a decent candidate from the former FWL RAT in FM: 3085. It carries a can opener (an HPPC) on only a slightly slower chassis. There's no TSM-enhanced brawler on the FWL RAT in FM: 3085, but the SR1-OG Strider G does appear, and the massed SRM salvo from its 14 MML tubes would fit the lance.
Hope this helps.