WNR3500L V1 Wireless Mode and Rate

Hi,

2 days ago I bought this amazing piece of hardware and I've already flashed Tomato Shibby build on it (latest one from 19/03 i think).

I have a few questions for you networking gurus:

1. Does using transmission affect the usage of the router in any other way except the up/down speed? (like decreasing rate or smth like that)

2. If I access the router remotely, the rate stays at 58/65 mbps. While using my laptop back home I see it constantly switching from 160 to 243 mbps and back. 

3. My Wireless Network mode doesn't have G/N Mixed mode, only Auto/B/G/BG Mixed/N only. Is that a Shibby firmware issue?

Thanks in advance.