I had a Torque 200 tune, sounded better, but to be honest, I didn't have the seat of the pants feeling that it was faster. Your mileage may vary. The tune lowered the cam changeover, but in retrospect, I liked how the original kicked in and you felt it. With the tune, you don't feel it as much, you just hear it changeover. Just my preferences. The most annoying thing about the tune was that it didn't always start the first time when engine is cold.
I'd stick with your M45 and just wait till it goes. I'm not sure where you get that it wasn't designed for repeated high rpms. I mean, it's factory right??? If it goes, then you instantly have an NA and then you can decide if you want to go rev300 or not (you definitely will btw). Another way is to lower your weight. Stock battery is 26lbs, I'm selling a 4lb LiFEPO4 battery if you are interested (shameless plug).
2005 Magnetic Blue Elise, Factory twin oil coolers, Sport pack with LSS wheels with 6.5 fronts, and touring pack with matching hardtop and insulated soft top. OEM stage II exhaust, carbon fiber intake, HID's, 5.25 and 6.5 Polks with JL Stealthbox and Alpine PDX-5 amp, Sony DSX-S310BTX head unit with Bluetooth, sector111 bootie and aluminum carpet buttons, OEM embellisher rings, shower cap and outdoor cover, factory painted console and AC shroud, battery cut off switch, factory starshield.