Mate - The tyre thing is really quite easy.
The Metz's are soft and if (like me) you tend NOT to throttle off for bends and actually lean over it is like abrading then with a sanding disk. They were listed (until Metzler USA withdrew the listing - Germany has never afaik listed the rim sizes) spec'd as optimal for 3.75" rim - not a 3.5". This is usually not a big issue plus/minus 1/4". Mine most certainly was NOT 150/80 fitted - was more a 143/90 - called a pinch fit. The Metz was designed as an H rated tyre - but does so well in the testing it can actually obtain a V rating. It would a be STUNNING tyre on something less like - well - a Rocket. I got 7700kms out of mine.
The Avon is spec'd for 3,5 rim - BUT they are NOT as grippy in the cold. This may or may not matter to you. I have had an Avon on and it too wore "cupped" But was a 150/80 fitted. It lasted LESS than the Metz as it improved my cornering speeds. Lasted about 6300kms. And this with (shock - horror) a CAR TYRE on the rear. Yes - High speed cornering on a square tyre - How dare I? - Lock up your daughters. This pre-dates the E-MAX availability in Europe. Otherwise I would have never known it works.
The E-Max is proving to be a spectacular tyre. Wearing evenly and remarkably slowly. I did put a but of a flat centre in it going to the UK and back, but it's back to rounded again.
NOW - I know this will make many cringe - but several of us tried using an MC rear tyre on the front. Avon had a good 140/80 Z rated called the AZARRO but is is discontinued. Some of us continue to run this way. Hedonists, heathens I know: I use a Bridgestone BT021 150/70 rear on the the front. I offer this as an option to consider. I know others have done even more extreme. This type of thing WAS commonplace on bikes with many tyres actually being bi (directional I mean). It is lasting like the E-Max - WAY more than expected.
The other option is to use marginally smaller width fronts and look for a higher speed rating. Metz do full Z rated 140/75R17 in Europe but it is NOT sold in the USA.
The only thing you REALLY need to watch - and
@1olbull has the data: Messing with tyre sizes on ABS bikes. With the E-Max (which is oversize in profile) on the rear, I am sure you cant go down much in size at the front. I find this web as a usefull tool to feed in different tyre sizes to compare rolling radius etc
Tire Size Calculator - Compare Tire Sizes | Tacoma World