Rolls-Royce (LSE: RR.) shares remain a winning investment. Even those taking a stake at the beginning of 2026 will have seen their money grow by around 30%.

Of course, the long-term returns have been magnificent. Anyone brave/lucky/skilled enough to invest five years ago will have achieved a potentially life-changing gain of +1,300%.

But as astonishing as it sounds, some UK stocks have done even better.

A former penny stock outpacing Rolls-Royce

Filtronic (LSE: FTC) is one example. In its own words, this business is a “designer and manufacturer of products and sub-systems for the aerospace, defence, telecoms infrastructure, space and critical communications markets“.

Now, you probably don’t need me to tell you that companies with exposure to these sectors have become incredibly popular. However, Filtronic’s performance has been truly eye-popping.

Helped by the rise in defence spending, not to mention becoming a supplier of technology to Elon Musk’s SpaceX, the share price is up over 2,300% from where it stood in August 2021.

However, Filtronic shares were once even higher than they are today.

Heavy faller

Some profit-taking might help to explain the massive pullback over the summer. Indeed, even a few directors have been selling stock. News that the company expected revenue to only be in line with analyst predictions may have also underwhelmed some.

On a positive note, there’s been better momentum in the last week or so. A rise of 16% since full-year numbers were announced on 4 August suggests that investors have now adjusted their expectations. Or have they?

Still frothy

One issue that even the most ardent supporter would probably concede remains the valuation. Despite the substantial fall in its share price, Filtronic still changes hands for 72 times forecast earnings.

For comparison, Rolls-Royce shares can be bought for the equivalent of 37 times projected 2026 earnings. Even that number makes me nervous. After all, the long-term average among UK stocks is somewhere in the mid-teens.

To be fair, CEO Tufan Erginbilgiç has done a stellar job of turning the latter around. Combined with the tailwinds mentioned earlier, this has allowed the FTSE 100 giant to keep announcing new contracts and continually raise guidance on earnings.

The only way that Filtronic’s price tag can be justified would be for its management to do the same thing. So, the market will be looking for evidence that its relationship with SpaceX is expanding but also that it’s diversifying its client base. Based on its most recent update, that seems to be happening. The question is whether the pace is sufficient.

Don’t bet the farm

For growth-focused, risk-tolerant investors looking for alternatives to Rolls-Royce shares, I can see the appeal here. Filtronic is a profitable company with technical expertise and a solid-looking order book. If all goes well, I wouldn’t be surprised if it continued to outpace the top-tier engineer.

Even so, I’m not brave enough to make it a sizeable part of my own portfolio. The huge fall earlier this year shows how quickly investors can take flight.

Tying in with its line of work nicely, I reckon this go-go stock might be one to consider as a smaller, satellite holding that exists alongside larger, more conservative investments.

Should you invest £5,000 in Filtronic Plc right now?

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Paul Summers has no position in any of the shares mentioned.