Just realize that 8” are going to be rather inaccurate unless you treat your room, and even then it’s going to be a bit much for the typical bedroom.
Accuracy doesn’t matter all that much while playing, not mixing. Also, room reflections don’t depend on monitor size at all. I don’t even know where this idea comes from. They depend on frequencies.
And when we get to frequencies, physics dictates that you MUST have a large speaker for low end. You can extend frequency range down by using ported cabinets (and most, if not all, monitors have that) but that comes at a price as it increases excursion and thus distortion. So, other things being equal, if you see two speakers with different woofer sizes and about the same frequency range the smaller one will simply sound worse.
Unless you play some easy acoustic stuff, you need the low end. If you play along some backing tracks with bass and drums, you really need low end.
Of course, there are bad speakers, good speakers and great speakers. Size isn’t everything. There will be smaller speakers with better low end than some bigger ones. But you need size nevertheless. It’s just a freaking law of nature. The less you depend on bass reflex ports or electronics, the more accurate low end you’ll get. 8” is better than 6”. 12” better than 8”. For a near field monitor and normal rock music or metal, you MUST have some low end. And that means 7 or better yet, 8 inches. 6 in some cases, depending on monitor.
Now, if you do real mixing work, it gets much more complicated. Because in mixing, you may want to sacrifice low end somewhat and care for midrange much more. There, with two way speakers, large woofers may not be beneficial, there’s also a whole big story about crossovers, Class D vs Class AB amps and so on and so on. But that’s mixing, not playing.
Now, about that “big speakers bad for small rooms” thing. Sorry, but that’s complete and utter bullshit. Speaker size has nothing to do with room acoustics, these things are independent. Whoever created this stupid urban myth deserves to burn in hell, and it’s astounding that so many people keep repeating it. What actually happens here is that small rooms are problematic for low end as it builds up pretty fast and you can’t always move away from places where it gets overwhelming. But. Think about it, how do small speakers help here? They don’t!!! They just produce less low end, that’s it. So your ears get more room reflection and less speaker. This means worse, less accurate “blanket covered” sound. If those small speakers have extended low end, you get poor sound from speakers, poor sound from the room and almost no good low end at all. That’s what you get. A bigger speaker at lower volume at a closer distance will give you better result!
Now to this treatment thing. You cannot realistically treat your bedroom for low end. You just can’t. Another law of nature, sorry. Doing it effectively would mean rebuilding the whole room, that’s way too complex and expensive.
What CAN help, if your room isn’t excessively small, is speaker placement. Moving away from corners, walls, trying different places, some experimenting. Standing waves don’t fill the whole volume there some are spots better than others. Do not place your speakers on the desk, raise them so you don’t get reflections from the desk surface together with sound coming from the speakers. Don’t place them against the wall. Room treatment will help with higher frequencies. Well, there are lots of advices you can find on the topic.
But do yourself a favor and if you just plan to play through those monitors get decently sized ones. If you want to do mixing work - that’s a much more complicated story.
And don’t spend a lot of money on these.
