I have measured a little over 12A of charging current on my setup (2×85W panels, each rated 4.87Imp & SunSaver MPPT-15 cont) using a Fluke multimeter. That is easily within the 20-25% advantage window I mentioned over having a PWM unit.
You are correct, the advantage is only realized during Bulk-stage charging, however that is the stage that returns the greatest amount of power into your battery. The quicker you can get your battery charged back up (and into Absorption mode), IMO the better it is for your whole system (especially if you happen to use up a lot of energy during the previous night).
I will say it again, a 170W panel w/PWM controller should work just as well as a 140W panel on a MPPT unit (and is cheaper). The OP's budget and/or space constraints are what will have to dictate which setup is best for his use.
Edit:
Perhaps it should be asked of the OP here before the thread strays too far off into this PWM vs MPPT thing...
What kind of loads are you planning to run with this solar setup? Fridge (size?)? LED lights? Computer? Car stereo most of the day? Other?
Maybe it might be worthwhile to tally up how many watt-hours or amp-hours you think you'll be using (if you haven't already), and figure out exactly how much solar it is you need.
A typical 40-50qt 12V fridge for example is likely to consume about 500-625 watt-hours on a warm day according to measurements I've taken on a couple units (kept out of direct sun). A 140W-capable solar setup should infact be enough for that however it might not leave much reserve for the running of other loads (playing the car stereo for example).
This is if you want to return a full charge to your battery the next day... If you don't plan on being parked for more than a couple days straight, then you can certainly get away with sizing your solar smaller.