MASSEY 135 TIRE SIZE, DOES IT MATTER???

I don't see stablility as being a big benefit of the wider tyres. If you are are so getting so near the limit of stability that the difference between 11.2 and 12.4 matters in practice, you are too close. As Jack says, widening the track gives the biggest benefit to stablility.

We've got everything from 10 x 28 to 14.9 x 28 on our 6 35's and 135's.

The differences are mainly in speed calibration for spraying and fertilizing - the larger sizes cover more ground at the same rpm. The 14.9's set the rear end a couple of inches higher, giving a nose down look. And a bit less ground pressure for travel on soft ground - often a factor on our sod fields.

We set up duals for soft ground, and that's fun - there are 10" rims and 12" rims, and the MF adaptors won't work with the 12" rims. Mixing and matching is tricky, so we can keep some space between the tires instead of having them chafing the sidewalls.

I think, but can't prove it, that the wider tires have a bit less slippage.

The stability Tom mentions - if you're facing this issue - can be addressed somewhat by setting the rear wheels a bit wider.

I guess I'd be less concerned than Tom about cancelling your order!