It's a hard question. I did this change, too, in my work. I migrated programs from Clipper5.2 to FP2.6. I agree with JanBucek, that a migrating from CLipper to FPDOS isn't a big advantage, but it's quite easy. But not problemlos. FPDOS can use the commands, procedures and functions a bit unlike to Clipper, so can confuse the new code. But generally FPDOS is compatible (from above) with Clipper, and can handle the memory better, than Clipper. It can be one reason.
The other, that further develop can use FP advantages.
FPW is similar to FPDOS, if FPDOS was written with SCREENS and REPORTS. In that case the migration from FPDOS takes only few time. An advantage can be the windows printing, and it can be a relevant reason for migrating.
Summa summarum: I guess, that you know the FoxPro, but not the Clipper. So a direct building from Clipper source code can give a running program, but after that come the "small" problems. But has worth a try.