Depending on what you plan to carry in your vest and how much of it; I would say that either a chest pouch system or plate carrier setup would be ideal. The reason is that it keeps everything in front so that things aren't conflicting with your waist strap from the pack. This setup also raises everything above the beltline which will be more comfortable (nothing sucks more than wearing strap on top of strap for 16 hours a day). Another advantage of this type of rig is that it is side-closing which keeps all the PALs real estate on the front, not wasting room for buckles and fasteners.
Anywho, I would suggest either a Weesatch (or a Wasatch if you've been hitting the donuts too much
) made by High Speed Gear Inc. or the Rhodesian Recon Vest by Eagle.
The Weesatch has a lot of versatility in that the internal magazine compartments can carry a variety of magazines for various calibers with its adjustable retention straps. The whole front surcface is covered in PALs to allow you to place any MOLLE-type pouch you want right on top of your mags. It is a plate carrier, so you can drop in hard ceramic or SAPI plates in the front and back. Another feature you would be interested in because of your pack situation is the fact that you can remove the rear compartment and run the shoulder straps crisscrossed over your back and attach them to the tri-glide buckles on the side of the front panel. If you opt to wear the back panel, I would highly suggest getting the enhanced shoulder straps at SKD Tactical as well as the HSGI Shoulder Pads.
I haven't had personal experience with the Eagle Rhodesian Recon Vest, but from what I've read, those who have it like it. It has pretty much all the same benefits as the HSGI Weesatch, except it doesn't come with a back panel (one can be purchased seperately) and it has no internal mag pouches. All mag pouches and accessories must be bought seperately. The benefit of this is more customized loadout at the expense of, well... more expense.
Both HSGI and Eagle have stellar reputations and make bombproof gear. Both companies are made in the USA! Both of these rigs also allow you to tuck the bib down/behind the sternum area if you aren't using plates. Check out these links:
http://skdtac.com/category.asp?CATEGORYID=163
http://skdtac.com/item.asp?ItemID=SKD6477&PRICE=175&CategoryNum=187
Hope this helps.