As a general rule Colt pistols have thinner slides and frames than much of the competition, which makes them feel really good in the hand but which also means there's less raw material to grind/file away when you're building a custom gun. I still remember an older Springfield I once had with a thick, squarish front strap that made the grip feel like I was holding a 2x4.
Yes, front strap thickness can vary on Colt's depending upon who did the machine work. The one pictured by Evolution is the thick version. The other version has a bevel on the inside bottom. Those are typically the thinner version. Those are the reason for the "panel cut" checkering style. On those, I would recommend staying with 25 or 30lpi. Don't think you need 20 just because you're a man's man. Well machined checkering like Evolution pictured is plenty grippy...even at 30lpi. Most people have felt a Kimber or Baer and think that 30 isn't very sharp. It's just that their checkering isn't very sharp. Well done 30lpi checkering is pretty sticky.
The Colt front straps with their "enhanced" magwell are only really thin at the bottom. The rest of the strap should be fine. A solution for that is to do Pete Single style overruns that terminate before the bottom or do a double border checkering pattern.
Not to Hi jack the thread but , Evolution Armory, is it right that you worked at Colt? If it wouldn't be too much to ask , could i pm you to ask you some questions about the series 70 reproduction model? thanks