Max "low altitude" airspeed is 230knots indicated air speed. I forgot the altitude that you can go faster... it's one of those "I don't fly that fast, so it doesn't matter to me". That's speed through the air, not "ground speed" (1 knot is 1.15 mph). Also, that's in "public" airspace. In restricted airspace (i.e military training zones), most of those rules are waived. I"m not sure if "every flight" has to "request permission" to waive that rule in a restricted space or if the restricted airspace has a blanket "go whatever speed you want", cuz I'm not military.
Dash, I'd highly recommend the instrument, that's where you actually learn to maximize your aircraft's capabilities, i.e. you really learn to fly-the-numbers, economize the plane and fuel. You'll be a far better pilot with it, than without... and if you're going to do that, you might as well tack on the commercial rating too. The commercial rating, basically, you need to learn an extra 3-4 maneauvers, and you learn that you can charge people to cover operating costs of the aircraft, but as soon as you charge more, you have to follow some other set of rules. I got em both (SEL & MEL, Instrument/Commercial). But quite frankly, I never bothered doing anything with Commerical (got it to have it, and got it in parallel with the Instruments). I've done some instrument flying, but aren't current, as I haven't kept up with the 666 rule. The instrument I remember the best was a 3 hour flight (from Columbus Ohio to NY City) in a single engine Cessna with a friend. We cruised at 9k feet asl and were in between cloud layers. That was sweet. A cloud layer below us, a cloud layer above us, unlimited visibility in between and not a single other soul in sight. That right there made the Instrument worth it. That flight ended with a localizer approach down to minimums, in the middle of a rainstorm. We got down to minimums, couldn't see squat but my friend could look down and see land (I didn't want to look straight down and possibly induce vertigo so I had to trust him, which I did), so since he could see the land, there wasn't anything around, we blew past mins by 70feet and finally broke out under the cloud base, in a driving rainstorm, 2 miles off the runway end... a quick slip and a bankity-bank to line up with the runway, and we landed pretty easily. It was pretty awesome if I must say so myself. Especially since I had to abort the first approach due to a comedy of errors on it.
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Also, the best thing about an instrument rating is that you can honest say the following to some random hottie: "Baby, I'll show you the sun on a rainy day, I'll give you the stars on a cloudy night". Cuz that's what you can do with an instrument rating. Honestly. Just file an IFR flight plan on a rainy-day/cloudy-night, and pop above the cloud layer. Then join the mile-high club.