My truck had a 40-series on it while I waited for my 50-series to be ordered.
It blew donkey balls! Droned like crazy in the cab between 40 and 55 mph. IMO, it's just too short a muffler to sound good on our trucks. The 50-series DeltaFlow sounds great... and, despite what the Magnaflow sack-riders say, all of the mufflers with similar dimensions sound pretty similar.
Speaking from experience... if you want to retain your sanity, DO NOT put the 40-series on your Tacoma.
EDIT** I forgot to add... since installing the muffler, my truck has consistently gotten roughly half a mile per gallon better gas mileage. I do A LOT of highway driving, so it was easy to see the mileage difference. Hell, in the couple of months I've had it, the gas savings is probably more than the muffler cost.