There are 32 available BUFG components that can span the entire SSI device. In VU9P, I got 240 BUFGCE in one SLR. How can I know which BUFG can span the entire SSI device.
All BUFGs can span the entire device.
However I would recommend reading the UltraFast Design Methodology guide, specially the section on Designing with SSI Devices, to help guide on the implication of SLR crossings.