Extremely mobile and when you combine the AMS with it's speed and maneuverability missiles should not be a problem. It is able to put serious pain on any target up close and light mechs especially could be in for a world of hurt due to Beagle and 4 streaks with ammo to spare. Use it's vertical advantage for best results.
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Way too much SSRM ammo. In my 3M build I find that 3 tons is more than enough. I don't think I've ever run out. Dropping down to 3 tons of ammo gets you a larger engine and nearly max armor. But personally I think you're gimping your potential a bit with all those jump jets. Yeah I like them too but I've been running my 3M build with 4 SSRMs and a Large Pulse Laser. But if you don't like that or already have a XL350 Engine and don't want to upgrade (I wouldn't blame you given the expense) here is a hybrid: That ER Large Laser version actually looks pretty good. That long range poke negates one of your weaknesses (lack of range) and will also help you farm C-bills because you'll get more kill assists if you're able to hit things earlier in the match. Try it out. I HIGHLY doubt you will run out of SSRM ammo.
Nice build, here are a few variations I'll been messing around with. Going 115 kph is nice but I find myself running out of ammo. Still got 826 dmg on my second game with 3 kills. I Think I may give this a whirl. It runs slightly cooler with some crit padding in the torso and an additional ton of ammo, sacrificing 6.5 kph. Or drop engine size again for some additional heatsinks.
Yea there is too much ammo there and the JJ's are a bit excessive but I felt like one of the unique aspects of the Griffin is that it can equip alot of JJ's and wanted to take advantage of that. You are right though the reason I use the XL350 is I already got one to use in my Victors and I try to use the same engine as much as possible to save credits. I will definitely give it a try with the Large Laser though to rack up some assists