For example, if you're going to have 15 pairs of 10g links on the 6509, this implies some 6700 series 10g cards, all of which are fabric only cards. A classic bus card and a fabric card can't even directly communicate, they have to bounce data transfers through the supervisor. Additionally, any classic bus card precludes the whole chassis from running in compact mode, halving (or more) the supervisor's PPS rate. Lastly, , you'll want to avoid sharing ASICs on a 6148 cards (I recall it's one ASIC per 8 ports).
Basically, again, you can use a 6148 but it can be very degrading to overall performance of the 6509, and since this is your core device, is that acceptable?
The reason I asked what else is in the chassis, if you already have any other classic bus cards in the chassis, adding another classic bus cards won't degrade the whole chassis further.
Personally, working with gig and 10g ports, in a distribution/core role, I recommend preserving compact mode. Additionally, a 3750-X may also perform better connected to a 6509 via dual 10g links than devices connected using a 6148 as it has 20 Gbps vs. 16 Gbps bandwidth.
PS:BTW, if you had a 6724/6748 line card, that would be the best way to connect the servers to the 6509..
