Interesting question. I would suggest waiting in your situation. That said, I think people here are thinking the next update will be more than it will really be. Lets look at a few things:
1. Montevina is a CHIPSET, that is, basically, a motherboard, NOT a processor. When Montevina comes out, the processor will still be PENRYN, the same processor in the current MBPs. The next new processor is NEHELEM ("Centrino 2"), which in my understanding is not due until 2009.
2. The only thing performance wise Montevina will change is the front side bus (FSB) speed. And while that is a difference, its not a huge one. There *may* be faster Penryn's out by then too, but all in all, I don't expect the CPU speed of the June MBPs to be that much above the current ones.
3. Speculation about video cards is just that - speculation. Right now, the 8600M GT is pretty much the best card you can find in a 15" notebook. The faster cards are found only in 8lb lug-a-book gaming laptops, because they draw too much power and put out too much heat. Whether this will change a lot by June is anyone's guess, but I'd tend to think not, unless Nvidia's release schedule shows something I don't know about. We may get an 8700M in June or something, but I don't expect a major GPU upgrade. Plus, knowing Apple, there is always the POSSIBILITY they will switch to ATI or something and we could end up with a card that is, for gaming applications, WORSE than the 8600M. That happened with the last iMac update, so its definitely not unheard of.
4. With the changed chipset, I would think a new case is likely in June. This is good if you don't like or are tired of the current case. But, at the same time, having the last of a line is not a bad thing always. The case AND the santa rosa platform in general is extremely fine tuned at this point.
One thing that is for sure though, whatever is released in June (IF anything is released) will likely be faster than the current MBPs.. probably not by a lot, but likely faster. If this computer needs to last you through college, I'd probably lean towards waiting, since you don't really need it now.