I did a Gen 4 to Gen 5/6 hybrid kinda... I didnt want to stretch the chassis to move the fuel tank like the Gen 6. Like others have said, price can get out of hand super fast if your not diligent on your budget and stick to it. My renovation got out of hand early on and just got financially...
I have the FRS4 and it's noisy... But it works awesome, shifts smoothly, and holds up to a fairly high amount of power. The main drawback is the cost of repair. Gears (especially the R&P) and parts are very expensive. Mine went 7 years before a full rebuild.