What hardware for 300 Mbps internet connection?

I work for a cable company and get free internet, currently my internet connection is 250 Mbps, but I ping at about 275 Mbps. Also, My company pushes up employee connection speeds about once a year or so. I want to build a Sophos XG home box but need to figure out what the best hardware would be for that. I want something that can pass 300 Mbps or greater and can possibly deal with a little internet speed increase down the road. My internal network is 1 Gbps. I also have cisco routers, switches etc and fiber on my network for CCNA learning, etc. and I'm running a Qnap Server and Windows servers... may be adding another Qnap as well. I need something that gives me good bandwidth on email, AV, firewall, pretty much all that I can get. I'm no too concerned about VPN, just the other stuff for security, blocking out china, etc. and want to ensure decent speeds. I've looked at the hardware guide to try to calculate, but as for CPU/Ram It still doesn't really answer the question completely, unless i'm getting actual Sophos Hardware.

I'm thinking of this:

Supermicro SYS-5018A-TN7B 1U server with A1SRM-LN7F-2758 Motherboard.

https://www.newegg.com/Product/Product.aspx?Item=9SIAB9458B6077 

Motherboard Features:
1. Intel® Atom processor C2758, SoC, FCBGA 1283, 20W 8-Core
2. 7x GbE LAN including 6 ports LAN bypass (SW programmable) ports w/SoC I354, I350-AM2 and I210-AT
3. 1x 3.5" Fixed drive bay or 4x 2.5" drive bays w/ optional bracket
4. 1x PCI-E 2.0 x4 (in x8) slot
5. Up to 64GB DDR3 1600MHz ECC or non-ECC UDIMM
6. IPMI 2.0 with shared LAN

I know that XG home only supports 4 cores and 6 GB of ram. So, the 8 cores is overkill, but that is ok and I would install 6 or 8 GB of ram on it. Also will install 120GB DOM, SSD or HDD.

The main question is, with 4 cores and 6GB ram limit, will this be able to provide the 300+ Mbps throughput I need? Is this a decent system and compatible hardware (especially for NIC's)?

It seems comparable to the XG 135 with it using the 4 cores and 6GB RAM only. Will it work? 

Thanks!

Tommy