In my opinion the V880 is a more superior server and your are looking at apples and oranges.
The technology changes in the 3 years from each of their releases are vast and wide(4500-April 1998 & V880-Nov 2001). Depending on application load both are good solid machines. It is true that the 4500 will hold 14 CPUs but of a slower speed(464MHz max, most common 400MHz, but we won't go there) and Ultra II. The V880 with Ultra III CPU is a better processor with a speed of min 750MHz and a max of 1200MHz.
Not to mention, and I not 100% sure, that the centerplane of the systems have got to be different. SUN never jumped on the +MHz(make a faster) CPU to impress customers kick unless it could increase performance.
Hope this helps.
Another couple of points probably worth mentioning; SF V880 supports more than twice the memory ( 64GB ) of the E4500 ( 28GB ) and the SF V880s I/O subsystem supports three 66MHz PCI slots. However the V880 was designed to upgrade the E450 and the SF4800 is the system that was designed to upgrade the E4500. The E4500 is a very good server though, I have worked with a number of customers that are using MySQL and >8 CPU/ 8GB RAM on the E4500, the performance is phenomenal!