If you're going to spend up to 600 on a suit, I'd go with a Ralph Lauren or a DKNY over Suit Supply. Not a fan of what they have to offer.
At $600, in my opinion go for a half canvassed suit at least. I'm not sure if RL or DKNY is Half-canvassed or fused at that price point.
To the OP:
The other option if you can afford to wait 3-4 weeks for it is going the Thick As Thieves route. Their
website isn't great but they produce really great suits. Most of the suits you see Wis (wj4) and Adrian (Pinoy732) are made by them. You have to measure yourself or if you are in LA they will measure you. I believe they start at $480 and max out at about $600. Best part they are fully canvassed suits. It is extremely difficult to find fully canvassed suits at that price. Although you may have through look through a few of their pages
here just on their first page along I saw variations of light grey. I'm sure you can find a gray option that can fit what you want.