For me this question is no-brainer. I would build my wheelset with a 7 speed Hyperglide freehub. I have a Shimano 6207 freewheel rim and it's heavier than the freehub counterpart. Also, It's pretty easy to take cassettes apart to make a custom cassette. All you need is the 7 speed spacers. I just did a search on Amazon and found a 12-28 7 speed cassette for 18 bucks.