Having just replaced the 11 1500uf Jackons on my Abit BE6-II, I noted the difference in size between these and the Panasonic FCs that I put in. It led me to thinking about why it's a problem to get 8mm caps in 1500uf, 6.3V. The third most important parameter when choosing capacitors in a design is of course the current rating. As CPUs have got faster, and the core is pulling out more big current pulses from the reservoir caps, then they will demand more current capacity from the caps. I haven't checked the current rating of the Jackons compared to the Panasonics, but maybe Panasonic are more conservative...

Back in my mainframe computer development days, hundreds of years ago, we were pretty proud we'd reached a 12 layer central processor backplane. But I see manufacturers now talk of 20 or more layers... Now on that sort of board, you really don't want to mess with the plated thru holes!

Whatever you do, don't use a drill to clear out holes, even if you think it's smaller. These are multilayer boards with internal planes, for at least ground and +V, in addition to the tracks you can see on each side. The holes are plated through and arranged to make contact where necessary with the internal tracks. Drilling could destroy these connections.
Mike