proportioning valve - adjustable v. self adjusting?

[sdkar]

I am buying my brake setup now and have a question.  I am using a stock booster and master cylinder setup. I have four wheel disc brakes.  What would be better or what are the pros and cons of using either an adjustable proportioning valve versus a self adjusting one?

Here are the two choices.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=7954132542

or

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=8070408299&ru=http://motors.search.ebay.com:80/?from=R40&satitle=8070408299&fvi=1

as always, opinions are appreciated.  You guys are helping my build my car...so thanks.

Steve

[JohnZ]

The first one (the combination valve) was used on most GM disc applications from the mid-70's on, but there were at least 20 different part numbers due to unique calibrations for different car lines, weights, and engine options for different disc/drum (with an RPV in the drum outlet) and disc/disc (with no RPV at all) applications. Who knows how this one is calibrated, and it's not adjustable - if it isn't right for your combination, you have to replace it with another one until you find the right calibration.

The second one is quite common - Wilwood and several others make these, and they're easy to calibrate/adjust yourself to make sure the fronts always lock up first.