What is your age? How much house do you intend to purchase? What is the employer match on your 401k? If you maintain your current saving strategy, how long will it take for your to reach your 100k down payment goal? Any other debt in the equation? Have you decided on a 15 year or 30 year mortgage (or some other duration)
63k is a nice downpayment on a reasonably priced home many regions of the country. You already have enough to avoid mortgage insurance on a home costing 315k or less. Because mortgage interest rates are likely to rise over the next year or two, you should calculate whether it makes sense to pull the trigger on a house with savings you already have. It might not pay off to wait and save if rates tick up and erode the advantage of making a larger downpayment.
Assuming that you do need or want to continue saving towards the 100k goal, then my advice is to contribute enough to your 401k at least enough to maximize your employer contribution, but no more. Throw whatever you can after that at other debt and saving for your goal.
IMO, the fact that rates are at near historic lows factors into your strategy.
Edit based on your comment:
If mortgage rates were near their historic average, I would recommend that you just be patient and stick with your current savings plan.
But that isn't the case. Rates are near historic lows and you are close to having 20% down on a 400k house, which eliminates the cost of mortgage insurance. If I was in your situation, I would reduce my down payment goal from 100k to 80k, and maximize my savings towards that goal in an effort to get a house purchased sooner rather than later. The downside is that you throw away some free money and delay getting your retirement savings ramped up. You can make up for this since you are only 26.
I don't feel qualified enough to give advice on converting to a roth and then borrowing against it. I will let others tackle that.