Hi Jack,
Welcome to the forum.
The Racer 2 at its new price of $725 and the Nox 6000 at $999 rrp, I think the Racer 2 is probably more closely in line with the X-terra 705, but I have personally owned both, and am an agent for both brands, so happy to do a a quick comparo:
Batteries:
Racer 2 runs on 4 x AAs, Equinox uses a built-in LiPo pack.
Coils:
Racer 2 comes stock with an 11x7" coil, Equinox comes with an 11" round
Racer 2 has about 8 optional accessory coils, Equinox has 2.
Weight/balance:
Both are about the same weight, but I think the Racer 2 is better balanced, mainly due to having some of the circuitry and batteries out the back under the armrest.
But there's also ergonomic differences with the straight shaft vs s-bend shaft, with fans of both, so this is very much a personal thing.
Waterproof'ness:
Equinox is rated to 3m (not the stock headphones), Racer 2 is not waterproof, only the coils.
Wireless:
Racer 2 has 2.4 Ghz wireless ability, but can only pair up with Nokta/Makro wireless headphones.
Equinox can pair up to Bluetooth or Low Latency Bluetooth, so you have many more options when it comes to headphones.
Frequency:
Racer 2 is using a common happy medium 14 kHz. This is perfectly fine for most coin and relic hunting.
Equinox 600 has a choice of 5, 10 or 15 kHz, or MultiIQ (multi simultaneous freq)
Performance:
This is a very tricky one, as a lot comes down to settings, and user experience, coil being used, how you are using the machines discrimination etc etc.
One key difference is that the Racer 2's recovery speed is pre-set for each mode. The Equinox 600's recovery speed is adjustable.
The MultiIQ is also very good on low conductors, and seems to have the sensitivity of a machine with a frequency closer to 30 kHz. On the beach the Racer 2 is very stable for a VLF, but ground balance needs to be at or close to zero, so some depth is lost. The Equinox works very well on wet salt sand - this is probably one of the biggest differences with Minelab multi-frequency machines.
In general terms, the Nokta & Makro machines like other Euro detectors are very fast machines with very little filtering, so they "talk" to you. You can really hear what is going on under your coil, but in saying this, the Racer 2 is one of the more tame units they've put out - not a roaring lion like the Fors Relic is/was. Minelab machines tend to be quieter running, but the Equinox with a fast recovery and high sensitivity can start to talk to you if that's what you want.
There are many other subtle differences and lots of similarities but I don't want this becoming an essay
Hope that gives you a better idea on some of the key differences.
Cheers, Nenad