Nebula California has some exotic cross world stuff you may be interested in.
For ground game stuff, I did a simulation with various rules for solo infantry. I did battletech, battledroids, a few editions of the btech RPG, DnD, 40k...
Upon running the scenario with the same troopers with different systems, the stats that diverged was
Range Vs Movement.
Turns to complete the scenario.
Complexity to describe the rules and events of the quick firefight.
If you want a 'Battletech' feeling game for the out of mech stuff, you want a lowish range to movement. Battletech is roughly a 1 to 3 scale, meaning an average trooper mech can move into melee range after being hit by the average ranged attack 3 times, if the other side doesnt move. So DND, for example, with 320 range shortbows and 60 range moves, is a 1 to 5.5 range, so ranged attacks over terrain are much more impactful--you can and will get cut to pieces on a large map in DnD style movement v range. The 3rd ed btech RPG on the other hand was a very low range, so you can run into melee range pretty quick, making ranged attacks even more point blank then battletech.
For turns to complete, this is kinda like how grindy the characters are. A time of war RPG is more or less rocket tag, where infantry die super quick when hit. Normal battletech is fairly grindy mech on mech, but solo infantry is ultimate rocket tag as any hit kills a trooper or ejected mechwarrior. Battletroops can take a few hits, but lucky hits still drop them in 1 shot.
Anyway, regardless of what rules you go with, if you want the out of mech RPG stuff to have a similar feel to btech, I found you want tankier characters that can die to unlucky hits, but otherwise can shrug off a few normal hits, and not too much range on ranged attacks so you can still make it to melee, but enough range that melee isnt the dominate focus of infantry combat.
