Wireless Intel Ultimate-N issues


I recently bought a new laptop from BTO (15M49) and I've been having trouble with my wireless connection. The first thing is that in task manager the link speed sometimes varies quite a bit (118mbps -300mbps or so). This might not actually be a problem but still wanted to mention it..
The main issue is that I rarely achieve my maximum internet speed (testing with ziggo.speedtest.nl) of about 50-52 mbps. it hardly ever goes above 46. Along with that, while I am downloading anything at that speed (46 or so mbps) it is nearly impossible to do anything else online. In that case I cannot even load my router's inlog screen.
This issue does not occur at all when I'm connected to the router by wire. My old laptop did not have this problem either.
Also, in adapter settings I turned IPv6 off as that seemed to make the link speed vary even more..

BTO 15M49 (MSI GT60 0NC)
Intel core I7 3610QM
12GB (3x4GB) Kingston HyperX DDR3-1600MHz
Killer e2200 Gigabit Ethernet
Intel Centrino Ultimate-N 6300: driver from BTO
Seagate 500GB +4GB SSD hybrid
Seagate 750GB HDD

I allready tried updating the driver to the latest on the intel site which had no effect, also all power saving options for the WLAN are turned off (in adapter settings and power options)

In adapter settings:
2.4GHz channel width: auto
802.11n mode: enabled
Bluetooth AMP: disabled
Fat channel intolerant: disabled
Mixed Mode protection: CTS-to-self enabled
preffered band: no preference
Roaming aggresiveness: medium
transmit power: 5.Highest
Wireless mode: a/b/g

My router is a draytek vigor 2130n with the latest firmware in n-mode only and WPA2 security on channel 7 and 3 which are not used by any other network in the neighbourhood (checked with Xirrus)
I allready tried turning WMM off in the router, which had no noticeable effect.

Laptop is obviously checked for virusses and spyware with Microsoft Security Essentials, Malwarebytes and Spybot

I hope someone can help me figuring this out,
Thanks in advance

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