Originally Posted by adamrice

Here's a sideways suggestion: rather than frankensteining together a cassette, change your chainrings. The OP was going for a 12-28, which has a slightly lower high end than the 11t that has become conventional.

If you've got a 52/36 in front, changing to a 48/32 is equivalent to switching from an 11t to 12t top end. If you've got a 50/34 in front, you'd change to 46/30 to get the same effect. You'd probably need different cranks for 46/30, but you would be able to mount 48/32 on typical road 4-arm road cranks. I've got 46/30 × 11-30; apart from an Easton crank, it's a Dura Ace drivetrain and it works like a charm. The front mech doesn't follow the curve of the chainrings perfectly, but front shifting seems fine.