If you've got an adequate head, it's probably enough. I had a 3030 head, but I found the QR system wobbly. You might want to go up one size or consider a Gitzo low-profile 3-way pan head, probably a 1370, which is not too outrageously priced at Robert White.
For 4x5" I usually use an old Leitz Tiltall. These can be had for around $100, about the same price as a new one, but the older ones are better made. Remarkably, I was just reading in the current issue of _View Camera_ (March/April 2003) that Steve Fitch uses a Tiltall for his Eastman 2D 8x10", often making exposures of 1 to 30 minutes. I usually use a bigger tripod for 8x10", but that's a real testament to the sturdiness of the Tiltall.